Amino Acids

Amino acids are the building blocks (monomers) of proteins. 20 different amino acids are used to synthesize proteins. The shape and other properties of each protein is dictated by the precise sequence of amino acids in it.

Each amino acid consists of an alpha carbon atom to which is attached

a hydrogen atom

an amino group (hence "amino" acid)

a carboxyl group (-COOH). This gives up a proton and is thus an acid (hence amino "acid")

one of 20 different "R" groups. It is the structure of the R group that determines which of the 20 it is and its special properties. The amino acid shown here is Alanine.

The Amino Acids
(For each amino acid, both the three-letter and single-letter codes are given. Click the name to see the structural formula)

Humans must include adequate amounts of 9 amino acids in their diet. These "essential" amino acids cannot be synthesized from other precursors. However, cysteine can partially meet the need for methionine (they both contain sulfur), and tyrosine can partially substitute for phenylalanine.

The Essential Amino Acids

Histidine

Isoleucine

Leucine

Lysine

Methionine (and/or cysteine)

Phenylalanine (and/or tyrosine)

Threonine

Tryptophan

Valine

Two of the essential amino acids, lysine and tryptophan, are poorly represented in most plant proteins. Thus strict vegetarians should ensure that their diet contains sufficient amounts of these two amino acids.

19 of the 20 amino acids listed above can exist in two forms in three dimensions. Link to a discussion.